The word "forgive*"(aphiemi-to send forth*) implies a legal action: it holds one 'harmless' from a legal debt. To be declared "aphiemi", means one's debt has been satisfied; in the case of Matt. 12:30-32, one's penalty of 'sin and blasphemy' shall be "aphiemi" them-following, of course, the prescription of 1 John 1:9,"If we confess our sins; He is faithful and just to forgive(aphemi) our sins, and to cleanse us from all unrighteousness."
Therefore, the consequence of Blasphemy Against the Holy Ghost is "ouk aphiemi" or "not forgiven". This implies impending legal action, in which a consequence of not satisfyng the debt has occured. In Mark 3:29, a parallel passage, the word "aphesis" denotes freedom or liberty, "ouk" in front of it means being held "bound for trial". We see this action in Matt. 18, when after the servant who owed his Master much, was forgiven; he instead refused to "hold harmless" one who asked him forgiveness, rather, (vs 30)"...he went and cast him into prison, till he should pay the debt."
The Master was furious when he found out servant whom He had "aphiemi" and "delivered him over to the tormentors, till he should pay all that was due Him."(vs 35) The debt was 10,000 talents-more than anyone could pay in a hundred lifetimes.
We see then the consequence for "Blasphemy of the Holy Spirit" is severe, and so it would be important to know what it means to do such a thing. We get the implication from the parallel account in Mark 3:30, where it says,"He hath an unclean spirit"; in other words, attributing the works of God which they saw before their own eyes, to the devil. To blaspheme God, is forgiveable; to blaspheme His Son, is forgiveable; the only way one can blaspheme the Holy Spirit is if the Holy Spirit is present, and then one blaspheme's that Presense(ie: attributes that Presense to Satan). The closest example we have of that is in Acts 5:3 where Peter tells Ananias,"Why hath Satan filled thy heart to lie to the Holy Ghost?" The consequence was immediate judgement, as Ananias fell down dead.
"Overlooking" does not carry a legal definition; when we are 'forgiven' we are set free from a legal obligation, of which there are legal consequences for not fulfilling. To be told "You are forgiven", is to be before the Court of Heaven, where the Lord is the Supreme Judge, and have your '10,000 talent debt' which is due cancelled, and now you are 'free to go' and enjoy your freedom.
Ref. for 'aphiemi' from letter of Demosthenes: If any man has remitted [aphiemi] to you any part of what was due him, no wrong is suffered by either party to the arrangement. But we have not remitted [aphiemil anything to you, nor have we consented to your voyage to Rhodes, nor in our judgment is anything more binding than the agreement.